This invention relates to an internal combustion engine and more particularly to a variable valve admission operating device for such engines.
In search of improving the performance of an engine, many systems that change the valve opening characteristics have been invented. Of such systems, those that allow a change in the amount of air entering the cylinder by gradually and simultaneously varying lift and duration, have demonstrated to achieve a sensible drop in emissions and energetic pumping losses, a faster throttle response and an increase in torque.
A series of disadvantages is present in almost all of those systems invented, as poor reliability, great complexity, high number of parts, high costs and difficulty of production, high energetic losses due to high reciprocating mass, high inertia, wear, noise.
Systems that allow a change in amount of air entering the cylinder by gradually and simultaneously varying lift and duration of the valve are known in the art. A device (according to Japanese Application Patent 2000-078134 U.S. Equivalent U.S. Pat. No. 6,425,357) that tries to address the problem of a link mechanism likely to be long and complicated, has also got its disadvantages. Some of the intermediate drive system parts are of very difficult construction, which renders the mechanism anything but economic to construct. Furthermore, the stopper pin (132a) is subject to very important loads compared to its size and, thus, its durability is questionable. Another characteristic is that the intermediate drive mechanism is composed from many big parts that have reciprocating motion, resulting in unacceptable reciprocating mass.
Another device (according to European Patent Office patent EP1143118) with an acceptable cost of construction, simplicity and reliability was effectively built and massively produced, obtaining significant advances in fuel consumption, emissions and torque. However, its limitation is still the high reciprocating mass of the arms (ref. 7) that drive the rocker arms, that causes undesirable energetic losses. Furthermore, its parts are complex and of difficult construction, requiring astonishing tolerances. These energetic losses increase rapidly as the engine speed increases which limitates the use of systems of this kind in low-displacement high-speed engines. Furthermore, a raise in engine speed generate bigger efforts, and thus bigger parts (increasing the reciprocating mass problem), or the need of much more expensive materials.
The principal objective behind this invention is, precisely, to obtain a design in which the reciprocating masses are greatly reduced, which would lead to a decrease in the energetic losses due to the movement of the reciprocating mass. It is also of the greatest importance the simplicity, reliability, strength and its simple and economical construction. The best way of reducing to the minimum the reciprocating mass is not to include in the reciprocating-moving parts the sub assemblies used to change the lift characteristics. In the second device (EP1143118), this happens, but those masses are still very high, due to the use of long arms. Searching for alternatives, the best one found was an oscillating camshaft as the way to change the valve lift.
The great breakthrough and what makes this system unique is the fact that the camshaft does not rotate on a fixed support in the cylinder head, but on a support which rotates around a main shaft. This means that the camshaft not only rotates but it translates up and down. By making this translation movement the valve lift and duration are increased or decreased.
It is, therefore, a principal object to this invention to provide an improved valve operating device for an internal combustion engine wherein a reduction in the complexity and the alternative masses is possible.
It is a further object to this invention to provide an economical, efficient, reliable and stepless variable valve lift and duration control mechanism for the valves of an internal combustion engine. It is a yet further object to this invention to provide an improved valve operating device for an internal combustion engine wherein an increase in performance (allows higher engine speeds than other similar systems and, thus, increases the power output) and a slight increase in fuel economy without increasing the production costs, or even lowering them, is possible.
This invention is a variable valve operating device for the valves of an internal combustion engine, capable of varying the lift, the opening and closing angles of the intake valves. And with an entirely new approach: the change in valve lift is achieved by means of translating the camshaft axis position. The result is an improvement in simplicity, production costs, reduction of reciprocating mass and reliability, compared to similar systems.
The variable valve operating device is composed by a camshaft that operates connected to the crankshaft through a pair of gears and a phase-difference varying device, a main shaft fixed on the cylinder head, one camshaft holder per cylinder that rotates around the main shaft. Also, a command shaft mounted on the cylinder head, which, by its moving, changes the angular position of all camshaft holders simultaneously, is provided. As a result, the camshaft axis rotates around the main shaft with an oscillating translation, driven by the command shaft. An intermediate arm per admission valve rotates around the main shaft and remains in contact with the cams of the camshaft by means of a spiral spring per cylinder. Each intermediate arm drives a rocker arm, which in turn drives the valve, keeping both in contact by means of a valve spring. Changing the position of the throttle pedal, a control system rotates the command shaft, which changes the camshaft position. This change displaces the extreme positions of the movement of the intermediate arms, thus changing the lift and the duration of the valve movement.